In the course of certain investigations undertaken by different research groups relative to the study of the constituents of natural galbanum essential oil, it became apparent that this essential oil contains certain non-terpenic hydrocarbons, in particular, undeca-1,3,5-triene.
This compound may occur under the form of one of the geometrical isomers of formula ##STR1##
A hydrocarbon with a non-terpenic skeleton and a very powerful odour was in fact isolated by Y. Chretien-Bessiere et al. from galbanum essential oil [cf.: Bull. Soc. Chim. France, 97 (1967)]. This investigation allowed assigning the structure of undeca-1,3,5-triene to the compound in question and to determine that it possessed a double bond with cis isomerism and a double bond with trans isomerism; however, the respective position of these double bonds in the molecule could not be determined. In a subsequent communication, Y. R. Naves [cf.: Bull. Soc. Chim. France, 3152 (1967)] confirmed the presence of undeca-1,3,5-triene in galbanum essential oil and assigned, by making use of a deep spectral analysis, the structure of the two isomers of the product in question, these isomers having been defined as the compounds of formula Ic and Id. However, these two compounds could not be isolated in their pure state. In fact, in an attempt to separate them by means of spinning band distillation columns, an easy dimerization of the compounds occurred. A separation by means of vapour phase chromatography or low temperature crystallization proved to be equally unsuccessful.
The finding that the product isolated from the hydrocarbons fraction of galbanum essential oil was essentially consisting of a mixture of two geometrical isomers of undeca-1,3,5-triene, was later confirmed by a study published subsequently by P. Teisseire et al. [cf.: Recherche, 16, 5 (1967)]. However, contrary to the results obtained by the previous authors, this latter publication discloses the presence in the galbanum essential oil of two hydrocarbon isomers defined as undeca-1,3 cis,5cis-triene and undeca-1,3cis,5trans-triene. The former of these compounds was considered to be, by the authors of this article, the odour principle of the essential oil [cf. also: Swiss Pat. No. 496,084].
The prior art, therefore, discourages the possibility of isolating and using as perfuming ingredients undeca-1,3trans, 5cis-triene and undeca-1,3trans,5trans-triene.
It has now been surprisingly found that the characteristic odour of galbanum essential oil is mainly conferred by the presence therein of undeca-1,3trans,5cis-triene (compound Ic). Though less developed, the odoriferous characters of the other isomer, undeca-1,3trans,5trans-triene (compound Id), present, nevertheless, a great interest for the perfumers. Consequently, the cited pure compounds find a useful industrial application on their own or in the form of mixtures of their geometrical isomers.
Galbanum essential oil develops a characteristic and particularly powerful odoriferous note of green type with a tonality reminiscent of dry wood of balsamic character [cf.: S. Arctander, "Perfume and Flavor Materials of Natural Origin", N.Y. USA (1960)]. Although it is used at small concentrations, this essential oil is particularly suitable, namely as ingredient in floral type compositions, such as for instance hyacinth, violet, narcissus, lavender or gardenia type compositions, wherein its "leaf" undertone develops or enhances the natural character.